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 Table of Contents  
ORIGINAL RESEARCH
Year : 2020  |  Volume : 12  |  Issue : 2  |  Page : 153-157

A comparative evaluation of tear strength and tensile strength of autoclavable and non-autoclavable vinylpolysiloxane impression material: An in vitro study


Department of Prosthodontics and Crown & Bridge, Manipal College of Dental Sciences, Manipal Academy of Higher Education, Manipal, Karnataka, India

Date of Submission22-Aug-2019
Date of Acceptance09-Nov-2019
Date of Web Publication28-Mar-2020

Correspondence Address:
Dr. Vinu T George
Department of Prosthodontics and Crown & Bridge, Manipal College of Dental Sciences, Manipal Academy of Higher Education, Manipal 576104, Karnataka.
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jioh.jioh_212_19

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  Abstract 

Aim: To evaluate and compare the tear strength and tensile strength of autoclavable vinylpolysiloxane impression material Affinis with non-autoclavable Aquasil. Materials and Methods: In this study, a total of 80 specimens of two vinylpolysiloxane impression materials (Affinis and Aquasil) were evaluated. Twenty specimens each for evaluating tear strength and tensile strength were fabricated for both Affinis Regular body (Coltene Whaledent, Altstatten, Switzerland) and Aquasil Monophase (Dentsply DeTrey, Konstanz, Germany). The specimens were randomly selected and divided equally between control (no autoclave or no disinfection) and experimental groups (autoclave or disinfection). All the samples were tested after 24h using an Instron Universal Testing Machine (Instron 3366, Norwood, Massachusetts) and were loaded until failure. The differences in mean values were compared with control group and were analyzed using independent sample t test (P < 0.05). Results: The results showed that autoclaving had no significant effect on tear strength and tensile strength of Affinis, and disinfection had no significant effect on tear strength and tensile strength of Aquasil. However, the tear strength and tensile strength of Aquasil before disinfecting was significantly higher than that of Affinis before autoclaving. A similar pattern was observed for disinfected Aquasil compared to autoclaved Affinis. Conclusion: Owing to no statistically significant effect of autoclaving on the tested properties of Affinis and no statistically significant effect of disinfection on the tested properties of Aquasil, these materials can be sterilized via these methods to eliminate all disease-causing microorganisms.

Keywords: Autoclaving, Disinfection, Tear Strength, Tensile Strength, Vinylpolysiloxane Impression Material


How to cite this article:
Gupta M, George VT, Balakrishnan D. A comparative evaluation of tear strength and tensile strength of autoclavable and non-autoclavable vinylpolysiloxane impression material: An in vitro study. J Int Oral Health 2020;12:153-7

How to cite this URL:
Gupta M, George VT, Balakrishnan D. A comparative evaluation of tear strength and tensile strength of autoclavable and non-autoclavable vinylpolysiloxane impression material: An in vitro study. J Int Oral Health [serial online] 2020 [cited 2020 May 28];12:153-7. Available from: http://www.jioh.org/text.asp?2020/12/2/153/281490


  Introduction Top


The success of prosthodontic treatment depends mainly on the precise fit of dental prosthesis, which itself is dependent on true and accurate detailed reproduction of intraoral structures. The impression material should not deform during the course of removal from the mouth.[1] Elastomeric impression materials have flexibility and offer high recovery during removal from the mouth.[1] In addition, silicones can be poured from a time of 2h from making the impression up to 1 week with the greatest change in their dimensional stability at any time being 0.3%.

When the impression materials are removed from the mouth, they are put through compressive as well as tensile forces. The overall tensile force is more than the overall compressive force during the process of extraction from undercuts, interproximal spaces, and so on. The susceptibility of impression materials to tearing is also enhanced in gingival crevices. The sterilization and disinfection procedures should not deteriorate the mechanical properties of the impression material.

Vinylpolysiloxane (addition silicone), an elastomeric impression material, is the preferred material for all impression procedures due to its excellent physical, mechanical, and biological properties.[2] Approximately 50% share in the impression material market has been captured by addition silicone materials.[3]

Different test methods are available to test tear resistance[4],[5],[6],[7],[8],[9] and tensile strength[6],[7],[8],[9] of impression materials, which makes it difficult to compare different materials. Several studies have focused on comparison of maximum elongation and tear energy (factor of tensile strength and elongation) of elastomeric impression materials.[6],[8],[9]

Dentists, including paramedical staff, are largely exposed to a wide range of pathogens and are among the high-risk group for a wide variety of diseases, including hepatitis B, human immunodeficiency virus, and tuberculosis.[2]

The American Dental Association and Centre for Disease Control have suggested several measures to prevent possible transmission of infectious diseases through infection control protocols. Some studies have shown that bacteria such as Escherichia coli, Enterobacter cloacae, and Klebsiella oxytoca are common and found in as many as approximately 67% impressions.[10] The risk of microbial contamination increases with the presence of blood stains in the impressions.

Attempts were made to produce sterile impression materials by adding disinfectants that inhibit the growth of microbes. However, it met with limited success. This was followed by the current practice of “immersion disinfection or spray disinfection” of the impressions after removal from the mouth, although studies have shown incomplete removal of potential contaminants. Immersion of the replica in a disinfection liquid is preferred as spray may not cover the entire impression surface evenly and adequately, but it can distort the impression materials that are hydrophobic.[11] Some researchers have suggested different disinfectants and different immersion periods for different impression materials.[12]

The best way to inhibit transmission of pathogens is to subject the impression to autoclaving immediately on its preparation but very few impression materials are compatible with autoclaving process.

In recent times, autoclavable impression materials, with superior properties, have been developed (e.g., Affinis impression material by Coltene Whaledent).

The purpose of this in vitro study was to compare the tear strength and tensile strength of newly introduced autoclavable vinylpolysiloxane impression material (Affinis) with a conventional vinylpolysiloxane impression material (Aquasil). We hypothesize that both the materials Affinis and Aquasil would show no deterioration in its properties after manufacturer-recommended autoclaving and disinfection protocols.


  Materials and Methods Top


An in vitro study was carried out to compare the tear strength and tensile strength of newly introduced autoclavable vinylpolysiloxane impression material (Affinis) with a conventional vinylpolysiloxane impression aterial (Aquasil) after procuring Institutional Ethics Committee clearance. The study was carried out over a period of approximately 1 year during 2017–2018 as part of MDS course of the first author.

Fabrication of metal mold

Aluminum mold was fabricated using computer numerical control milling machine, Model DTC 300 (AMS; Ace Micromatic Group), in accordance with the American Society for Testing and Materials specifications. The aluminum mold has a base into which impression material was dispensed and a lid that was assembled on top of the base.

Mold for tear strength

A metal mold representing the rectangular-shaped specimen of dimension 70 mm in length, 10 mm in width, and 1.9 mm thickness was prepared for measurement of tear strength. An indentation was created in the middle of the mold along its length and a triangular notch (90°) was pushed in this indentation along the width [Figure 1].
Figure 1: Metal mold of tear strength specimen representing rectangular-shaped specimen of dimension 70 mm in length, 10 mm in width, and 1.9 mm thickness for measurement of tear strength

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Mold for tensile strength

A metal mold representing the dumbbell-shaped specimen of dimension 115 mm in length, 25 mm in width, and 2 mm thickness was prepared for measurement of tensile strength [Figure 2].
Figure 2: Metal mold of tensile strength specimen representing dumbbell-shaped specimen of dimension 115 mm in length, 25 mm in width, and 2 mm thickness for measurement of tensile strength

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Preparation of impression material specimen

A total of 80 samples were prepared altogether. Of 80 samples, a total of 40 samples were prepared from Affinis. Of 40 samples, 20 specimens were rectangular shaped for measuring tear strength and 20 were dumbbell shaped for measuring tensile strength. Of the 20 specimens each for tear strength and tensile strength, 10 specimens were randomly selected and allocated to the control (no autoclave) group and autoclave group. A similar strategy was used for Aquasil, and randomly selected samples were allocated to control (no disinfection) and disinfection groups. A flow chart showing the study design is shown in [Figure 3].
Figure 3: Flow chart illustrating study design describing the entire study design (self reported)

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Tear strength and tensile strength determination

All the specimens selected underwent testing. The specimens were fastened on to the Instron Universal Testing Machine. The specimens were fastened at both ends by pneumatic clamps. Initially, the jig was adjusted to keep the sample at rest. Thereafter, loading was started in tension and was continued till it failed.

Tear strength determination

The rectangular specimen strip was mounted on the Instron machine, clamping both its ends. The machine was calibrated to move at a uniform crosshead speed of 10 mm/min. The movement was continued till tear commenced and was retained. The force required to commence the tear was recorded electronically. Tear strength is calculated as: Tear strength = Force (Newton)/Thickness (mm).[13]

Tensile strength determination

The dumbbell-shaped sample strip was mounted on the Instron machine, clamping both its ends. The machine was calibrated to move at a uniform crosshead speed of 50 mm/min.[2] A force of 50N was applied to pull the sample to reach the breaking point. For uniformity, samples that failed at gage length were considered. Samples that failed at other sections such as junction of reduced and grip sections were not considered. The built-in software of the Instron Universal Testing Machine recorded the tensile strength of the samples.

Statistical analysis

The mean ± standard error of the mean was determined, and independent sample t test was performed to evaluate the tear strength and tensile strength. Microsoft Excel Office 365 (Microsoft Corporation, Redmond, Washington, United States) was used to carry out statistical analysis. A value of P < 0.05 was considered significant.


  Results Top


Tear strength

Tear strength (N/mm) of Aquasil control was significantly (P < 0.05) higher than Affinis control. Also, tear strength of Aquasil disinfection was significantly (P < 0.05) higher than Affinis autoclave. However, no significant difference was observed between Aquasil control and Aquasil disinfection (P = 0.138) as well as between Affinis control and Affinis autoclave (P = 0.086) [Figure 4].
Figure 4: Graph depicting tear strength (N/mm) of tested specimens showing tear strength (N/mm) of Aquasil control was significantly (P < 0.05) higher than Affinis control. Also, tear strength of Aquasil disinfection was significantly (P < 0.05) higher than Affinis autoclave (*, shows significance)

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Tensile strength

Tensile strength (MPa) of Aquasil control was significantly (P < 0.05) higher than Affinis control. Also, tensile strength of Aquasil disinfection was significantly (P < 0.05) higher than Affinis autoclave. However, no significant difference was observed between Aquasil control and Aquasil disinfection (P = 0.410) as well as between Affinis control and Affinis autoclave (P = 0.943) [Figure 5].
Figure 5: Graph depicting tensile strength (MPa) of tested specimens represents tensile strength (MPa) of Aquasil control was significantly (P < 0.05) higher than Affinis control. Also, tensile strength of Aquasil disinfection was significantly (P < 0.05) higher than Affinis autoclave (*, shows significance)

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  Discussion Top


The performance of impression materials in obtaining accurate details of intraoral structures and precise fitness is of paramount importance in determining the success of prosthodontic treatment. The dentists and associated laboratory personnel are at high risk and vulnerable to contract transmitted diseases through direct or indirect contact with the patients, instruments and equipment, treatment materials, surroundings, and so on.[12],[14] There is a growing tendency to sterilize the impressions immediately on removal from the oral cavity to make it free from all forms of living organisms, whether pathogenic or not, to provide protection from diseases. The safety of dental professional has led many researchers to focus on the ways to disinfect the impressions. The standard sterilization and disinfection protocols should be followed to maintain the properties of impression materials.

The general practice to disinfect the impressions is either to spray disinfectants over them or immersing them in a disinfectant solution. But disinfection does not eliminate all microbes. Sterilization is the only way to eliminate all pathogens and make the impressions safe to use. Vinylpolysiloxane impression materials, particularly Affinis by Coltene Whaledent, have come to be known as a material that can withstand steam autoclaving. This study was conducted to assess the effects of autoclave sterilization on the mechanical properties of the autoclavable elastomeric material Affinis and compare it with the mechanical properties of non-autoclavable elastomeric material Aquasil after disinfection.[15],[16],[17]

As is known, the accuracy of fit and intraoral structures determines the ultimate outcome of the prosthetic treatment. When the impression material is removed from the mouth, especially from interproximal spaces, sharp line angles, and gingival crevices, both compressive and tensile forces act on it. The tolerance to these forces and ability to withstand deformation define the quality of the impression material. Any defect in the impression compromises the accuracy and quality of final restoration. Tear strength and tensile strength were considered important factors in this study because tear resistance (or tear strength) is a measure of how well a material can withstand the effects of tearing, whereas tensile strength is a measurement of the force required to pull something to the point where it breaks.

Required tensile strength of various impression materials has not been reported and hence is unknown. Recently, a study reported that a force of 224–514N is required to remove the impression from the mouth. Thus, the impression materials should withstand forces in this range without causing deformation of the impression.

The goal of our study was to determine the tear strength and tensile strength of autoclavable vinylpolysiloxane impression material Affinis and to compare it with the properties of conventional non-autoclavable vinylpolysiloxane impression material Aquasil after disinfection. The results showed that autoclaving Affinis did not significantly alter the tear and tensile strength compared to the Affinis control. A similar result was observed for disinfected Aquasil compared to the Aquasil control with no statistically significant difference between their tear strength and tensile strength. These results are in accordance with the manufacturer’s instructions of Affinis and Aquasil where they suggested safe autoclaving of Affinis and disinfection of Aquasil for infection control. However, Millar and Deb,[13] in a study in 2014, not only found out that autoclaved Affinis showed a considerably higher tear strength over the control Affinis specimens but also suggested that the difference was clinically acceptable. On the contrary, a later study by Kotha et al.,[2] in 2016, concluded that statistically no appreciable difference was observed in the tensile strength of autoclaved Affinis and control Affinis specimens, and also, no statistically significant difference was observed in the tensile strength of disinfected Aquasil and control Aquasil specimens.[2] These results by Kotha et al.[2] are again in accordance with our observations.

In addition, a study by Pang et al. in 2006 showed that 50% of dentists would prefer impression materials that could be autoclaved.[18] On the contrary, our results showed that the tear strength and the tensile strength of a disinfected material (Aquasil) were significantly higher than those of an autoclavable material (Affinis). These results indicate that Aquasil is potentially a better impression material in terms of mechanical properties compared to Affinis based on tear and tensile strength.

Moreover, further research should be carried out to evaluate the effect of autoclaving Affinis and disinfecting Aquasil on microbial growth compared to their respective controls as well as each other. These results will help us determine whether it is worth autoclaving/disinfecting Affinis and Aquasil or the material picked solely based on its tear and tensile strength. Such studies should also be carried out on other elastomeric impression materials available in the market.

Conclusion: The tear strength and tensile strength of Affinis (autoclavable vinylpolysiloxane impression material) and Aquasil (non-autoclavable vinylpolysiloxane impression material) remains the same even after autoclaving it. Lastly, the tear strength and tensile strength of Aquasil before disinfecting is significantly higher than Affinis before autoclaving, and the tear strength and tensile strength of Aquasil after disinfecting is significantly higher than Affinis after autoclaving.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Re D, De Angelis F, Augusti G, Augusti D, Caputi S, D’Amario M, et al. Mechanical properties of elastomeric impression materials: An in vitro comparison. Int J Dent 2015;2015:428286.  Back to cited text no. 1
    
2.
Kotha SB, Ramakrishnaiah R, Devang Divakar D, Celur SL, Qasim S, Matinlinna JP. Effect of disinfection and sterilization on the tensile strength, surface roughness, and wettability of elastomers. J Investig Clin Dent 2017;8. doi: 10.1111/jicd.12244.  Back to cited text no. 2
    
3.
Craig RG, Powers JM, Wataha JC. Dental Materials: Properties and Manipulation. 8th ed. St. Louis, MO: Elsevier; 2003. p. 175.  Back to cited text no. 3
    
4.
Herfort TW, Gerberich WW, Macosko CW, Goodkind RJ. Tear strength of elastomeric impression materials. J Prosthet Dent 1978;39:59-62.  Back to cited text no. 4
    
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Craig RG, Hare PH. Properties of a new polyether urethane dimethacrylate photoinitiated elastomeric impression material. J Prosthet Dent 1990;63:16-20.  Back to cited text no. 5
    
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Chai J, Takahashi Y, Lautenschlager EP. Clinically relevant mechanical properties of elastomeric impression materials. Int J Prosthodont 1998;11:219-23.  Back to cited text no. 6
    
7.
Hondrum SO. Changes in properties of nonaqueous elastomeric impression materials after storage of components. J Prosthet Dent 2001;85:73-81.  Back to cited text no. 7
    
8.
Salem NS, Combe EC, Watts DC. Mechanical properties of elastomeric impression materials. J Oral Rehabil 1988;15:125-32.  Back to cited text no. 8
    
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Klooster J, Logan GI, Tjan AH. Effects of strain rate on the behavior of elastomeric impression. J Prosthet Dent 1991;66:292-8.  Back to cited text no. 9
    
10.
Powell GL, Runnells RD, Saxon BA, Whisenant BK. The presence and identification of organisms transmitted to dental laboratories. J Prosthet Dent 1990;64:235-7.  Back to cited text no. 10
    
11.
Johnson GH, Drennon DG, Powell GL. Accuracy of elastomeric impressions disinfected by immersion. J Am Dent Assoc 1988;116:525-30.  Back to cited text no. 11
    
12.
Thouati A, Deveaux E, Iost A, Behin P. Dimensional stability of seven elastomeric impression materials immersed in disinfectants. J Prosthet Dent 1996;76:8-14.  Back to cited text no. 12
    
13.
Millar BJ, Deb S. Effect of autoclave sterilisation on the dimensional stability and tear strength of three silicone impression materials. Open J Stomatol 2014;4:518.  Back to cited text no. 13
    
14.
Abdelaziz KM, Hassan AM, Hodges JS. Reproducibility of sterilized rubber impressions. Braz Dent J 2004;15:209-13.  Back to cited text no. 14
    
15.
Holtan JR, Olin PS, Rudney JD. Dimensional stability of a polyvinylsiloxane impression material following ethylene oxide and steam autoclave sterilization. J Prosthet Dent 1991;65:519-25.  Back to cited text no. 15
    
16.
Millar BJ. Dimensional stability of addition cured silicone impressions following autoclave sterilisation. J Dent Res 1999;78:297.  Back to cited text no. 16
    
17.
Olin PS, Holtan JR, Breitbach RS, Rudney JD. The effects of sterilization on addition silicone impressions in custom and stock metal trays. J Prosthet Dent 1994;71:625-30.  Back to cited text no. 17
    
18.
Pang SK, Millar BJ. Cross infection control of impressions: a questionnaire survey of practice among private dentists in Hong Kong. Hong Kong Dent J 2006;3:89-93.  Back to cited text no. 18
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]



 

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